Unloader for compressors



April 13, 1954 J. H. ANDERSON 2,675,172

. UNLOADER FOR COMPRESSORS 7 Filed March 22, 1946 2 Sheets-Sheet l I N V E N TO R (James Ii-A Hahn-{01; I

H I S ATTORNEY.

April 1954- J. H. ANDERSON UNLOADER FOR COMPRESSORS 2 Sheets-Sheet 2 Filed March 22, 1946 HIS ATTORNEY.

Patented Apr. 13, l9 54 UNLOADER FOR COMPRESSORS James H. Anderson, Easton, Pa., assignor to Ingersoll-Rand Company, New York, N. Y., a corporation of New Jersey Application March 22, 1946, Serial No. 656,318

1 Claim.

This invention relates to compressors, and more particularly to an unloader for compressors operated by constant speed drivers, such as synchronous electric motors, which are not readily adapted to actuate a compressor piston at different velocities for changing the capacity of the compressor.

One object of the invention is to equip the compressor with a durable unloading device that is reliable in action and requires a minimum of parts of simplified construction and which may be readily maintained with a minimum of attention to assure their efiicient action throughout prolonged periods of service.

Other object will be in part pointed out hereinafter.

In the drawings accompanying this specification and in which similar reference numerals refer to similar parts,

Figure 1 is a longitudinal elevation, partly broken away, of a portion of a compressor having the invention applied thereto,

Figure 2 is a view similar to Figure 1 showing a modified form of the invention, it

Figure 3 is a transverse view taken through Figure 2 on the line 3-3,

Figure 4 is an elevation, in section, of a detail, and

Figure 5 is a transverse view taken through Figure 4 on the line 5-5.

Referring to the drawings and at first more particularly to Figur 1, designates the compressor and 2| its casing which is bored to provide a compression chamber 22 the end. of which is closed by a head 23.

Within the compression chamber is a reciprocatory piston 24 for compressing the fluid medium, and in the wall of the compression chamber is an inlet valve 25 for controlling the flow of the fluid medium from an inlet chamber 26 into the compression chamber. In this form of the invention all the fluid discharged from the chamber 22 passes through a discharge port 21 into a clearance chamber 28, thence through a suitable discharge valve 29, a discharge chamber 30 and a conduit 3| to a storage receiver 32.

In accordance with the practice of the invention, communication between the compression chamber 22 and the clearance chamber 28 is controlled by a clearance control valve mechanism 33 that serves the additional function of unloading the compressor. The valve mechanism 33 comprises a casing 34 having an external flange 35 to seat upon the outer surface of the casing 2|. The discharge port 21, and. which is in conpart obvious and in stant communication with the compression chamber 22, is positioned in the inner end of the casing 34, and in the side of said casing is an opening 36 to open the interior of the casing 34 to the clearance chamber 28. On the inner surface of the end wall of the casing 34 is an upstanding flange 31 that encircles the port 21 and supports the valve mechanism 33 which is clamped against the flange 31 by a cover 38 that is pressed against the valve mechanism by a bolt 39 threaded into a plate 49 overlying the outer end of the casing 3%.

The valve mechanism 33 comprises a pair of valve seats 4! and 42 that engage the flange 3i and the cover '38, respectively, and are secured together by screws 43. The major portions of the opposed surfaces of the valve seats 4| and 42 are inclined to define therebetween a V-shaped space 43 which is the operating range of a valve element 45 clamped between the valve seats adjacent the closed end of the space 44.

The inclined surfaces on the valve seats 4| and 42 constitute seating surfaces 46 and 47, respectively, for the valve 45 which, in a preferred form, comprises a plurality of spring-fingers 48 that control the adjacent ends of ports 49 and 50 in the valve seats 4| and 42. The valve element 45 is preferably constructed of a single straight plate so that the fingers 48 will occupy a mid-position in the space 44 when the valve is inactive.

The fingers are lifted against the seating surface 4'! by pressure fluid flowing from the compression chamber 22 to the clearance chamber and are actuated in the opposite direction by pressure fluid supplied thereto from the storage receiver 32. Such pressure fluid is conveyed from the receiver by a conduit 51! connected to the bolt 39 which has a passage 52 extending therethrough to register with a port 53, in the cover 38, opening into the interior of the cover 38 which constitutes a pressure chamber 55.

The pressure value of th fluid thus introduced into the pressure chamber 54 is varied in accordance with variations in pressure, above a predetermined value, in the receiver: during partial load of the compressor, the pressure in the chamber 54 is varied progressively in inverse relation to progressive variations in pressure in the receiver; at full load the pressure in the chamber 54 is receiver pressure; and at no load the pressure in chamber 54 is atmospheric pressure. The regulator 55 performing thi function is interposed between the branches 56 and 57 of the conduit 5|. In the position of the regulator, as

shown in the drawing, the branch 51 is connected to the casing '8 at a lower elevation than the branch 56, and communication between the branches takes place through the bore 59 in the casing. The casing 58 is further provided with an exhaust port 60 located below the branch conduit 51 to afiord communication between the bore 59 and the atmosphere.

Within the bore 59 is e, reciprocatory valve iii of the spool type having a pair of heads 82 and 63 which are so spaced with respect to each other that, in the position which the valve occupies normally, the head 63 will cover the exhaust port 60 and the head 62 will lie above the branch conduit 56 to permit of free communication between th branches 55 and 51 of the conduit El. More specifically, the distance between the inner end surfaces on the heads '62 and tt is equal to the distance between the upper edges (as viewed in Figure l) of the port Eli and the port in the casing 58 registering with the branch conduit 56. Thus, as the head 62 moves downwardly to restrict the ilow of compressed air into the bore 59 from the conduit 56, the head 63 simultaneously moves to uncover th port til. The position of the valve M is determined by a spring 64 in the lower end of the casing 53 interposed between the valve and a spring seat 55 which may be raised or lowered, as by means of a screw 66, to condition the valve for controlling movement responsively to different pressures in the receiver 32.

On the upper end of the valve is a stem ii! that is connected to the central portion of a flexible diaphragm 68 that is clamped between the easing 58 and a cover 69 of cup-shape, the interior of which constitutes a pressure chamber l9 and is in communication with the receiver through a conduit ii.

In operation, and assuming the pressure within the storage receiver 32 to be below the predetermined maximum value for which the regulator 55 has been set, all the fluid medium compressed by the piston 25 is discharged through the port 21 and the valve mechanism 33 into the clearance chamber 23 whence it passes through the discharge valve 2t and the associated channels into the receiver 32.

The fluid passing through the valve seat 45 actuates the valve 55 against the seating surface H and holds it in that position until the piston 24 begins its suction stroke. At this point in the cycle of operation the pressure within the pressure chamber 5t, and which is conveyed thereto from the receiver by the conduit 56, will return the valve fingers it to the seating surface it and cut-off communication between the clearance chamber 28 and the compression chamber 2.2. The inlet valve 25 will then open to admit fluid into the compression chamber from the inlet chamber 26.

The valve mechanism 33 will continu to operate in the manner described and communication will exist uninterruptedly between the storage receiver 32 and the pressure chamber till until the receiver pressure predominates over the force exerted by the spring G l. When this predetermined maximum value is attained the fluid acting against the diaphragm 58 will depress the valve 6| to reduce the flow of pressure 'fiuid into the bore 59 and to uncover the exhaust port 8:}. The pressure chamber 54 will then be in communication with the atmosphere thereby reducing somewhat, depending on the degree of opening of the port 60 and the port registering with line 56, the

pressure in the chamber 54; and thereafter the valve fingers 33 will remain seated against the seating surface 4'5 until the pressure in the compression chamber 22 equals that prevailing within the chambered. The inherent resiliency of the valve fingers 43 will then cause them to snap back toward the seating surface at. This movement of the valve fingers will take place at any point in the suction stroke of the piston at which the pressures within the clearance and pressure chambers equal each other, and when, during this stroke the pressure of the fluid in the compression chamber falls below that prevailing in the inlet chamber 25 the inlet valve 25 will admit a new charge of fluid into the compression chamber.

The point in the suction stroke at which the valve action occurs is controlled by the degree of opening of the port (iii and of the port in the casing 58 registering with the conduit 5'E-the degree of opening of said ports is, in turn, dependent on the receiver pressure. the receiver pressure progressively increases, above the aforesaid predetermined value, the valve 5| is actuated in accordance with this increase to progressively throttle the flow of pressure fluid from the receiver 32 through the conduit 56 and progressively increase the degree of opening of th port 5%. With this arrangement then, as the pressure within the receiver 32 increases above some predetermined value, the regulator 55 acts to decrease, in proportion, the pressure in th chamber 54. The converse function also occurs-as the receiver pressure decreases towards said predetermined value, the valve ti moves to uncover the downstream end of the conduit 5 3 and restrict the flow through the exhaust port Eli, thereby increasing the pressure within th chamber 5%. Thus the regulator 55 acts in response to variations in receiver pressure, above said predetermined value, to vary in inverse proportion the pressure in the chamber 54.

Whenever the pressur within the storage receiver 32 falls below that exerted by the spring 84 the said spring will shift the valve ti to reestablish communication between the branch con-' duits 56 and 5? and to close the exhaust port (it.

The compressor is then again conditioned for the" delivery of its entire discharge output to the storage receiver.

Figures 2 and 3 difiers from that previously described in the respects that a discharge valve mechanism H2, or mechanisms, and which may be of any suitable type, serves as the sole flow controlling element between the compression cham ber and the storage receiver, and the valve mechanism 33 serves the single function of controlling. the compressor load. 7

During. the pumping action of the piston 2d compressed fluid passes both through the discharge valve i2 and through the valve mechanism 33. In view of the small capacity of the clearance chamber as compared with the storage receiver and the channels leading thereto the valve mechanism 33 will then operate in the That is, as-

same manner as in the form of the invention previously described. On each compression stroke of the piston 24, the valve fingers will be lifted by the fluid in the compression chamber 22 and enough fluid will pass into the clearance chamber 28 to compensate for the slight reduction incident to the flow of fluid from the clearance chamber to the storage receiver through the conduit 5!.

When the predetermined maximum pressure is reached in the storage receiver 32 the pres sure fluid in the pressure chamber 19 will act against the diaphragm 69 and depress the valve 6!, thereby conditioning the valve mechanism 33 to perform its load-controlling function.

I claim:

In an unloader for a compressor, a casing having a compression chamber, a piston therein, a receiver for the fluid compressed by the piston, a discharge valve for controlling communication between the compression chamber and the receiver, a clearance chamber, a clearance control valve means to control communication between the compression chamber and the clearance chamber comprising a cage having a pressure chamber and opposed seating surfaces, a valve in the cage to cooperate with one seating surface for controlling communication between the compression and clearance chambers and to cooperate with the other seating surface for controlling communication between the pressure chamber and the clearance chamber, the third said valve being constantly subjected to the pressure prevailing in the compression chamher for moving the third said valve away from said one seating surface to establish communication between the compression and clearance chambers, means for supplying pressure fluid from the receiver to the pressure chamber for returning the third said valve to said one seating surface, and means acting responsively to pressure in the receiver for controlling the pressure value of the fluid in the pressure chamber.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 831,522 Reardon Sept. 18, 1906 1,150,915 Wikander Aug. 24, 1915 1,607,531 Haight Nov. 16, 1926 1,614,138 Longacre Jan. 11, 1927 1,614,143 Metzgar Jan. 11, 1927 1,621,913 Longacre Mar. 22, 1927 1,918,891 Barrett July 18, 1933 1,969,076 Hirsch Aug. 7, 1934 2,032,429 Metzgar Mar. 3, 1936 

